The present invention relates to a continuously variable transmission for a vehicle, in which the power from a prime mover is divided by a power dividing mechanism and transmitted to a hydraulic continuously variable transmission apparatus and to a transmitting means for mechanical transmission of power, and the power from the hydraulic continuously variable transmission apparatus and the transmitting means is collected and outputted.
Conventionally, such a transmission is already known by, for example, Japanese Patent Application Laid-open No. 8-74965.
Although such a continuously variable transmission is capable of continuously varying the speed of the power from a prime mover and transmitting it to the driving wheel side by hydraulic power transmission with excellent continuous speed variability and by mechanical power transmission with excellent transmission efficiency, it is desirable, where a better fuel consumption performance is required in constant high speed traveling during cruising or the like, to make the power transmission by the hydraulic continuously variable transmission apparatus ineffective which is less than excellent in transmission efficiency, and to transmit the power only by mechanical power transmission. Therefore, it is conceivable, when a minimum gear ratio is to be achieved, to forcedly stop the operation of the hydraulic pump in the hydraulic continuously variable transmission apparatus to make ineffective the power transmission by the hydraulic continuously variable transmission apparatus, eliminate the drive loss in the hydraulic continuously variable transmission apparatus, and improve the fuel consumption performance by mechanical power transmission by a power dividing mechanism and transmitting means.
However, if the gear ratio intended for achieving the maximum speed (a greater gear ratio than the minimum gear ratio) is to be achieved only by mechanical power transmission by the aforementioned power dividing mechanism and transmitting means, the driving force may be insufficient and the maximum speed may be impossible to achieve, depending on the vehicle performance such as the prime mover output, vehicle weight and traveling resistance; or if the maximum speed is to be achieved with the hydraulic continuously variable transmission apparatus, though it becomes possible to secure a suitable gear ratio for achieving the maximum speed, the driving force may also be insufficient and the maximum speed may be impossible to achieve because the hydraulic continuously variable transmission apparatus is less than excellent in transmission efficiency.